PhCH2X 1 CH2=CHCH2X 30 2° CH3 Sw1,S2都快 SN1 Sxl、Sx2 SN2 SN2 (CH3)3C-CH3CH2- (CH3)2CH-CH3- R p-π共轭，加强了C-X键， H2C=CH 难断裂，一S、1,S2都难。 Organic ChemOrganic Chem PhCH2X CH2=CHCH2X 3º 2º 1º CH3 SN1,SN2都快 SN1 SN1、SN2 SN2 p-π共轭，加强了C-X键， 难断裂，—SN1，SN2都难。 (CH3 )3C - (CH3 )2CH - CH3CH2 - CH3 - SN1 SN2 X H2C CH X